[clang-cl] Fix PR38934: failing to dllexport class template member w/ explicit instantiation and PCH

The code in ASTContext::DeclMustBeEmitted was supposed to handle this,
but didn't take into account that synthesized members such as operator=
might not get marked as template specializations, because they're
synthesized on the instantiation directly when handling the class-level
dllexport attribute.

llvm-svn: 342240

2 files changed, 20 insertions, 0 deletions

diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index b107e8bd2a3..3d0d1e666cd 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -9724,6 +9724,14 @@ bool ASTContext::DeclMustBeEmitted(const Decl *D) {
         cast<FunctionDecl>(D)->getTemplateSpecializationKind() ==
             TSK_ExplicitInstantiationDefinition;
 
+    // Implicit member function definitions, such as operator= might not be
+    // marked as template specializations, since they're not coming from a
+    // template but synthesized directly on the class.
+    IsExpInstDef |=
+        isa<CXXMethodDecl>(D) &&
+        cast<CXXMethodDecl>(D)->getParent()->getTemplateSpecializationKind() ==
+            TSK_ExplicitInstantiationDefinition;
+
     if (getExternalSource()->DeclIsFromPCHWithObjectFile(D) && !IsExpInstDef)
       return false;
   }
diff --git a/clang/test/CodeGen/pch-dllexport.cpp b/clang/test/CodeGen/pch-dllexport.cpp
index 9c6623be436..b8db075046d 100644
--- a/clang/test/CodeGen/pch-dllexport.cpp
+++ b/clang/test/CodeGen/pch-dllexport.cpp
@@ -57,6 +57,13 @@ extern template void explicitInstantiationDefAfterDecl<int>(int);
 template <typename T> T __declspec(dllexport) variableTemplate;
 extern template int variableTemplate<int>;
 
+namespace pr38934 {
+template <typename T> struct S {};
+extern template struct S<int>;
+// The use here causes the S<int>::operator= decl to go into the PCH.
+inline void use(S<int> *a, S<int> *b) { *a = *b; };
+}
+
 #else
 
 void use() {
@@ -81,4 +88,9 @@ template void __declspec(dllexport) explicitInstantiationDefAfterDecl<int>(int);
 template int __declspec(dllexport) variableTemplate<int>;
 // PCHWITHOBJVARS: @"??$variableTemplate@H@@3HA" = weak_odr dso_local dllexport global
 
+// PR38934: Make sure S<int>::operator= gets emitted. While it itself isn't a
+// template specialization, its parent is.
+template struct __declspec(dllexport) pr38934::S<int>;
+// PCHWITHOBJ: define weak_odr dso_local dllexport x86_thiscallcc dereferenceable(1) %"struct.pr38934::S"* @"??4?$S@H@pr38934@@QAEAAU01@ABU01@@Z"
+
 #endif